1. Field of the Invention
The present invention relates to an atomic layer deposition (ALD) method and a semiconductor device fabricating apparatus having improved processing time.
2. Discussion of the Related Art
Electric devices are recently highly integrated to have smaller size including the vertical dimension. Specifically, a dielectric layer of a memory capacitor for a dynamic random access memory (DRAM) device and a gate insulating layer of a thin film transistor (TFT) device are developed to be thinner and thinner in the vertical dimension.
Under the design rule of 0.13 μm or less, new materials substitute for conventional ones to satisfy new electric qualities for devices fabricated under the same design rule. For example, instead of a heat-treated oxide film (usually, a silicon oxide film heat-treated under oxygen condition), a high dielectric film made of Al2O3, HfO2, ZrO2, or the like is selected for the above-mentioned gate insulating layer. For the dielectric layer of the DRAM, instead of a silicon nitride film formed by a chemical gas phase deposition, a very thin film made of a high dielectric compound such as barium-strontium-titanate (BST) or lead-zirconium-titanate (PZT) is selected.
A metal organic chemical vapor deposition (MOCVD) method was conventionally applied to fabricate the conventional thin films including silicon oxide or silicon nitride. However, because the MOCVD method is not suitable for fabricating the new thin films including BST or the like and having a thickness of about 100 Å (angstrom), new methods are developed. An atomic layer deposition (ALD) method is a typical example of the new methods.
In the MOCVD, various vapor substances are simultaneously applied to a substrate and deposited thereon to form a thin film. In the ALD method, however, various vapor substances are alternately and repeatedly applied to a substrate such that a plurality of atomic layers are sequentially deposited on the substrate to form the thin film. Recently, the ALD method is widely used to fabricate thin films of a semiconductor device.
In case of the ALD method, the thin film grows depending on a surface chemical reaction. Accordingly, though if the substrate has an irregular shape, the thin film grows uniformly on the substrate. In addition, because the thin film grows in proportion not to time but to number of cycles each sequentially providing a group of vapor substances, thickness of the thin film can be controlled precisely.
In FIG. 1, a reaction chamber 100 of an ALD apparatus according to a related art includes a lower housing 110a and an upper housing 110b, which provide a reaction zone 102 isolated from an exterior condition. Material gases are sequentially provided into the reaction zone 102 through an injection hole 140 in alternating orders. At this point, each material gas flows parallel to an upper surface of a substrate 130, which is mounted on a susceptor 120 disposed in the reaction zone 102.
A conventional method of forming aluminum oxide (Al2O3) film using the above-described reaction chamber 100 was suggested in page 3604, volume 71, Applied Physics Letters, 1997. In the reaction chamber 100 heated at a temperature of 150° C. (.degrees. C.), the substrate 130 is maintained to have a temperature of 370° C. Then, tri-methyl-aluminum [Al(CH3)3], purge argon (Ar), water vapor, and further purge argon (Ar) are sequentially injected into the reaction zone 102 for 1, 14, 1, and 14 seconds, respectively, thereby composing a cycle. The cycle is repeated as shown in a graph of FIG. 2. A vertical axis of the graph implements a processing time. However, because the graph is conceptual, each period of the cycle is not proportional to its length.
The above-explained method according to the related art has some problems.
Because the growth of the thin film is proportional to the number of cycles, a total processing time can be shortened by shortening the time of one cycle. However, because the conventional reaction chamber adopts valves to control the flow of each vapor substance, time delays occur due to a residual response time of the valves. In another aspect, after each vapor substance fills the reaction zone and reacts with the substrate, it is exhausted out of the reaction chamber and another vapor substance is injected into the reaction zone. The above-mentioned injecting and exhausting take some time, thereby making it difficult to shorten the time of one cycle. That is to say, the growth of the thin film is very slow in the reaction chamber according to the related art, which means that productivity of the conventional ALD method is very low.
In addition, in the reaction chamber according to the related art, the deposition occurs due to just a simple contact between the substrate and the vapor substance that flows parallel to the substrate. Accordingly, a deposition rate of the vapor substance is very low, which causes a poor productivity.
Some modifications were suggested to solve the above-explained problem of low productivity.
First, if a plurality of substrates, instead of just one, are mounted in the reaction zone, a simultaneous deposition can be applied for the plurality of substrates. Second, a plurality of reaction chambers, instead of just one, may be included in the ALD apparatus for the same purpose.
In case of the first modification, the reaction chamber should be sufficiently enlarged to contain the plurality of substrates. The large reaction chamber, however, causes a slow exhaustion of the vapor substance, such that a gas phase reaction of the exhausting vapor substance may occur in the reaction chamber.
In case of the second modification, each of the plurality of reaction chambers should be connected with a vapor supply pipe that provides vapor substances. Therefore, the ALD apparatus becomes to have a complicated configuration, which causes a high cost of the ALD apparatus.